Proteins PDF

What are Proteins.. ? -Proteins are Organic Nitrogenous compounds. C,H,O N (16%) -Other elements, such as sulfur, phosphorus and iron, are essential constituents of certain specialized...

What are Proteins.. ? -Proteins are Organic Nitrogenous compounds. C,H,O N (16%) -Other elements, such as sulfur, phosphorus and iron, are essential constituents of certain specialized proteins. Casein ( milk protein ) Hemoglobin (oxygen-transporting protein of blood) phosphorus Iron -Proteins are made of linear chain(s) of amino acids. x Amino acids x x x x x Units (monomers) x x x x x x x x x x x x x x Protein Chain (Polymer)  H x x Amino acids The smallest unit of protein (monomers) Chemical structure: Cental Carbon atom(α-Carbon) C COOH Amino group (–NH2) Carboxyl group (-COOH) R ▪variable group ▪confers unique Hydrogen atom (-H) chemical properties of the amino acid Alkyl group (-R) H H C COOH C COOH H Glycine CH3 Alanine  H R Peptide bond H R H N C C OH H N C C OH H O H O + H2O (Condensation reaction) x x x x dipeptide Peptide bond - The term protein is applied to describe molecules greater than > 50 amino acids - Molecules contain less than < 50 amino acids are termed peptides  Types of bonds in Proteins Covalent bond Non-covalent bonds - Strong ( Chemical ) - Weak ( Physical) Ex. Peptide bonds Ex. 1 Hydrogen bonds - Strong, chemical bond - Weak, physical bond between the amino group of one amino acid between the O-atoms of carboxyl group of one & the carboxyl group of adjacent amino acid. peptide chain & H-atoms of amino group of adjacent peptide chain. ( Not affected by denaturation) ( Affected by denaturation) Ex. 2 Ionic bonds - weak, physical bond between the oppositely charged groups & atoms. ( Affected by denaturation)  Classification of Proteins Classification of Proteins Based on Chemical and Physical properties: - Proteins are classified into three main groups as follows: 1- Simple proteins. 2- Conjugated proteins. 3- Derived proteins. 1- Simple Proteins On hydrolysis, they produce only amino acids. Albumin Myosin Collagen Keratin (egg white) (muscles) (Skin & bons) (Nails & Hair) Elastin Glutelins (Wall of the lung) (Wheat)  2- Conjugated Proteins Formed of protein part and non protein part 1-Glycoproteins: Proteins conjugated with carbohydrates e.g. Hormones e.g. ABO blood groups 2- Phosphoproteins : Proteins conjugated with phosphoric acid e.g. Casinogen ( in milk) e.g. Vitellin (in egg yolk) 3- Metalloproteins: Proteins conjugated with metals e.g Insulin (protein + Zink) e.g Ferritin (protein + Iron) 4- Lipoproteins: Proteins conjugated with Lipids e.g LDL (Low Density Lipoprotein) e.g HDL (Hight Density Lipoprotein ) 5- Nucleoproteins: Proteins conjugated with nucleic acid e.g Chromatin in chromosomes (protein + DNA) 6- Chromoproteins: Proteins conjugated with Colored metal e.g Chlorophyll with green color (protein + Magnesium)  3- Derived Proteins Denaturation of simple or conjugated proteins Change of the native state of protein as a results of exposure to a denaturing factor Causes (factors of denaturation) : 1- Physically; - Force - High temperature - High pressure - Radiation X-rays , UV-rays 2- Chemically; - Strong acid - Strong base - Organic solvents - PH Changes